This invention relates to systems for printing franking or postal impressions on mail and other items to indicate that a charge for handling the item has been accounted for.
Franking machines for franking items of mail by printing an authorised franking impression on the mail item are well known. In such machines the impression printed comprises an invariable pattern determined by the postal authority together with a variable part which indicates data variables such as a postage charge for the item and the date on which the impression is printed. The invariable pattern usually includes data identifying the franking machine and the postal office responsible for receiving mail items franked by that machine.
It will be appreciated that the printing of a franking impression on a mail item represents a charge for handling that item and hence it is necessary that proper accounting is carried out in respect of printing of such franking impressions. From the point of view of the postal authority, revenue from postage charges in respect of franked mail items is determined by the accounting carried out in respect of printing of franking impressions on mail items. Accordingly the postal authority needs to be assured that the accounting is properly and exactly carried out so that the postal authority can ensure that the correct revenue is received for mail items handled by the postal authority. Similarly the user of a franking machine needs to be assured that the charges paid to the postal authority are correct in respect of the franked items of mail.
The postal authorities require manufacturers of franking machines to take such steps as may be necessary to eliminate or at least reduce to an acceptable minimum the risk of fraudulent use of franking machines. Accordingly such machines are constructed in a secure manner with those parts of the machine concerned with carrying out accounting functions and setting of a postage charge value to be printed being housed in a sealed secure housing to which access by authorised personnel only is permitted and evidence of any unauthorised access is provided for example by breakage of a seal.
However while fraudulent use of franking machines can be reduced or eliminated by appropriate construction of the machine a further possibility of fraud on the postal authority is the use of copying machines capable of printing in a colour, corresponding to that of inks used in franking machines, to print copies of a single franking impression printed by a franking machine. With the common availability of copying machines capable of producing copies of franking impressions which are difficult to distinguish from genuine franking impressions printed by franking machines this is of major concern to postal authorities.